High intensity focused ultrasound (HIFU) has emerged as a precise, non-surgical, minimally-invasive treatment for benign and malignant tumors. At focal intensities (1000-10000 W/cm2) that are 4-5 orders of magnitude greater than that of diagnostic ultrasound (approximately 0.1 W/cm2), HIFU can induce lesions (i.e., localized tissue necrosis) at a small, well defined region deep within tissue, while leaving intervening tissue between the HIFU transducer and the focal point substantially unharmed. Tissue necrosis is a result of tissue at the focal point of the HIFU beam being heated to over 70° C. in a very short period of time (generally less than one second). Tissue necrosis also results from cavitation activity, which causes tissue and cellular disorganization. HIFU is currently being used clinically for the treatment of prostate cancer and benign prostatic hyperplasia, as well as the treatment of malignant bone tumors and soft tissue sarcomas. Clinical trials are currently being conducted for HIFU treatment of breast fibroadenomas, and various stage-4 primary and metastatic cancerous tumors of the kidney and liver.
Uterine fibroids are benign tumors of the uterus that cause abnormal uterine bleeding. The incidence of fibroids in women in their reproductive years has been estimated to be 20-25%, although autopsy studies show an incidence to be greater than 75%. Approximately ⅓ of women experiencing uterine fibroids will have a tumor that is symptomatic requiring treatment. Approximately 30% of all hysterectomies are related to the presence of uterine fibroids. Current treatment methods for uterine fibroids include both drug therapy and surgery. Experience with drug therapy shows almost a 100% rate of tumor reoccurrence once the drug therapy has stopped, and the drug therapy has numerous undesirable side effects. The rate of reoccurrence is significantly less for the surgical therapy (about 15%). Unfortunately, most current procedures for removing uterine fibroids are based on invasive surgical techniques, which require a significant recovery period and involve significant risks (such as blood loss, damage to related organs, and the ever present risk of infection). It is estimated that uterine fibroid procedures in the United States alone account for 1.2 to 3.6 billion dollars in annual medical costs.
It appears that HIFU, delivered using a transvaginal transducer, could provide a minimally-invasive treatment for uterine fibroids. On Oct. 22, 2004, the United States Food and Drug Administration (FDA) approved the ExAblate 2000™ System; a new medical device that uses magnetic resonance image (MRI) guided focused ultrasound to target and destroy uterine fibroids. While MRI guided HIFU therapy offers an alternative to more invasive surgical techniques, MRI equipment is very expensive, not nearly as available as ultrasound imaging devices, and not nearly as portable as ultrasound imaging devices. It would be desirable to provide a less costly alternative to MRI guided HIFU therapy. Such treatment is expected to compare favorably with the costs for the current drug related therapy for the treatment of uterine fibroids and its efficacy should compare favorably with the higher success rate of the current surgical procedures, but without the attendant risks.